Mettig was second in command of OKW/Chi.
Here is the relevant information :
What about Russian? It was known before the war and was multichannel transmission. This was read. It was only a mixing of eight to fifteen channels. There was no other encipherment. This unmixing was done at Wa Pruef 7, This was located at Staats under Colonel KARN, taken PW in Africa, assisted by Baurat KIERKHOFF. The specialists in speech encipherment who worked there were Drs. LIEBKNECHT and LOTZE. The man who worked on unscrambling Russian T/P was Dr. ??Schellhos?? , who was however basically a D/F man.
Why did I put the question marks? The text in that part is corrupted :
Strangely the rest of the report is fine….
I think it says Schellhos .According to this source Dr. Hans Schellhoss worked for Wa Pruef 7 and was an expert in Direction Finding equipment.
So another piece of the puzzle solved…